The Power of Cascade Testing and How Genetic Counselors Can Help

Amy Curry Sturm, MS, CGC, LGC

I’ll never forget the day I sat across the table from a mom and her two adult daughters, one of the daughters herself a new mom of a baby boy. That day, I was able to give the three women some very good news: neither the two daughters, their children or future children were at risk for a life-threatening heart condition called Long QT syndrome.

The family’s journey to learn more about their health through genetic testing began because 15 years earlier, the mom’s son (brother to the two sisters) died suddenly from Long QT syndrome - an inherited heart rhythm disorder that can lead to sudden cardiac death. He was just a young boy then, and his family wanted to know if the same fate might await them and future generations. In order to figure out whether the son’s Long QT syndrome had an identifiable genetic cause, we started with clinical genetic testing on his affected mom and grandfather. By doing this clinical genetic testing, the causative mutation in the family was found. Long QT syndrome is inherited in an autosomal dominant fashion, which means for close relatives of affected individuals (parents, siblings, children) there is a 50 percent chance to also have the same genetic predisposition. The two sisters were at a 50 percent risk for the mutation.

What is cascade testing?

The two sisters I met with had undergone a type of genetic testing called cascade genetic testing. Cascade genetic testing is one of the most effective and cost-efficient ways to identify individuals who are known to be at risk for an inherited condition such as heart disease and cancer. It’s the process of testing through a family in a specific order to identify all of the relatives who did, or did not, inherit a genetic mutation that is causing the condition of concern in the family. After the causative mutation has been identified in an affected person in the family, cascade testing is done in a stepwise fashion, which means at-risk relatives undergo testing until all relatives with the familial predisposition have been identified.

Cascade genetic testing is also a powerful tool to identify those family members who didn’t inherit the familial predisposition, like these sisters, and therefore are not at risk for passing on the condition. If they didn’t inherit the causative mutation, their children cannot inherit it either and would not be at risk to develop the condition.

Sometimes genetic testing can’t identify the specific genetic mutation associated with the condition of concern in a family. In this case, you may undergo other methods of cascade testing, called cascade clinical screening. These include non-genetic evaluations such as cholesterol values, mammograms, colonoscopies or other clinical tests, depending on what condition is running in a family.

What steps are involved and how do genetic counselors help?

Cascade testing is recommended if you have a family member who has a genetic mutation associated with risk for hereditary types of heart disease, cancer, and other conditions. If your doctor does suggest cascade testing, you and your family members can see a genetic counselor to learn more about the following important steps to cascade genetic testing and screening. Before you undergo testing, your genetic counselor will do the following to help with the cascade testing process:

Review your affected family member’s genetic testing result so that the right cascade genetic test can be ordered.

Construct a three to four generation family tree to document all relatives in the family who may be at risk for the condition running in the family.

Based on the family tree, identify all at-risk relatives, and specifically, which relatives should undergo genetic testing, or clinical screening, first.

Talk through the family’s dynamics and relationships, and brainstorm ways to help with communication about the testing process, genetic testing results or genetic diagnoses.

Develop and provide personalized tools to share with at-risk relatives, such as family letters, family emails and social media messages, and help them learn more by sharing any available condition-specific brochures.

Encourage you to talk with your relatives about finding genetic counseling services for themselves. Findageneticcounselor.com can be used to identify a genetic counselor in their area or to find telegenetic counseling options.

The Power of Cascade Genetic Testing

When I shared the good news with the three women, I remember the overwhelming relief and joy on the mom’s and daughters’ faces. Knowing that her daughters didn’t inherit the deadly condition that took the life of her beloved son was especially priceless and emotional information for this mom.

I worked extensively with this family over the years, and not everyone’s cascade genetic testing was negative. For those who tested positive, we scheduled appointments with our expert cardiology team. Even though the results weren’t “good news” for those family members, the team provided them with clinical cardiology screenings and potentially life-saving management, including the recommendation to take a daily medication to keep their hearts safe.

Genetic counselors: Here for You and Ready to Help

Genetic testing, and the results that come from it, can be powerful, yet emotional tools. Communicating with family members who may be at risk, including one’s own children, can be one of the most difficult conversations that individuals who undergo genetic testing may need to have. For example, for the mom I mentioned above, it brought back up all the emotions of losing her son again; however, by doing so, she likely saved the lives of other loved ones in the family.

Genetic counselors are here to help provide guidance to patients and their family members during these times. Since knowledge is power for so many hereditary conditions, we want to equip families with all the right tools they need to learn, and act on, the potentially life-saving information that can be gleaned from genetic testing, and the cascade genetic testing and screening that may follow. Find a genetic counselor in your area by using the “Find a Genetic Counselor” tool from the National Society of Genetic Counselors.

Amy Sturm, MS, CGC, LGC is a cardiovascular genetics expert and President-Elect for the National Society of Genetic Counselors and a Professor and the Director of Cardiovascular Genomic Counseling at the Geisinger Health System Genomic Medicine Institute.

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